1. Field of the Invention
The invention relates to a pattern forming method of a semiconductor device, and more particularly to a pattern decomposition method which is capable of achieving complicated layout patterns, which are conventionally achieved by a triple-exposure method, by double exposure.
2. Description of Related Technology
As one of the methods for increasing a resolution with the same wavelength as a numerical aperture (NA) of an exposure system, a double-exposure technique has been developed. A double-exposure technique involves decomposing complicated patterns so as to firstly expose one pattern and secondarily expose the other pattern. Such a semiconductor manufacturing method using double exposure commonly includes two mask processes and two etching processes. In other words, the desired patterns are completely formed in such a manner that the first mask and etching processes are performed and then the second mask and etching processes are performed.
One of the most important factors of the double-exposure technique is to perform the decomposition of a target pattern adequately for the double exposure, i.e., so as not to expose the adjacent patterns at the same time. It is easy to decompose patterns including simple lines and spaces. But when the target pattern includes a complicated layout, the patterns can not be adequately decomposed by double exposure, i.e., it is virtually impossible to practically achieve the independent pattern or the short patterns on the wafer. To this end, patterns having complicated layouts are often decomposed into three groups of patterns so as to apply a triple-exposure method (not the double-exposure method).
As described above, double-exposure methods cannot achieve complicated layout patterns on the wafer. However, when triple-exposure methods are used, one more mask should be fabricated and many processes, such as an exposure process, an etching process, a cleaning process, a deposition process, and the like, should be added. Accordingly, manufacturing costs and turn around times increase.